The broad objectives of this continuation proposal consist of three extensions of the program of study in the currently funded project. The first extension is from the study of a population of beginning readers to the study of a population of older, more fluent readers. The specific aims associated with this extension of our currently funded project are to: (a) determine whether the nature of phonological processing abilities, and the direction and magnitudes of their causal relations with reading, change as children move from initial acquisition to fluency in reading; (b) examine the consequences of individual differences in phonological processing abilities and decoding on subsequent reading comprehension; and (c) to resolve an important ambiguity about the apparent lack of a causal role for decoding in the subsequent development of phonological processing abilities. We will achieve these specific aims by a program of continued study of our existing longitudinal sample of approximately 250 children. The second extension is from the study of normal development to the study of abnormal development. The specific aims associated with this extension of our currently funded project are to: (a) examine the nature of the phonological processing abilities of children with dyslexia (specific reading disability); and (b) examine possible causal relations between the atypical development of phonological processing abilities and the development of dyslexia. We will achieve these specific aims by carrying out a four-year longitudinal correlational study of 120 dyslexic children. The third extension is from an exclusive reliance on longitudinal correlational studies to a combination of longitudinal correlational studies and training studies designed to manipulate levels of phonological processing abilities. The specific aims associated with this extension of our currently funded project are to: (a) use a training-study methodology to test the alternative models of the structure of phonological processing abilities and their causal relations with reading that we examined in our longitudinal correlational studies; (b) examine the degree to which phonological abilities are modifiable through training and the duration of such training effects, if found; and (c) examine the extent of differential response to training, and to identify individual difference variables that predict differential response to training. We will achieve these specific aims by carrying out a training study involving 200 kindergarten students who will be followed through second grade.